An engine may be operated with charge dilution to lower engine emissions and improve fuel economy. Charge dilution can reduce engine pumping work and cylinder combustion temperature, thereby improving engine operation. However, if an engine is operated at a high level of charge dilution and there is a rapid change in operating conditions (e.g., a change in engine load), the engine may suffer poor combustion stability and/or misfire, thereby causing poor drivability and/or increasing engine emissions.
The inventors herein have recognized the above-mentioned disadvantages and have developed a method for improving engine operation during transient operating conditions. One embodiment of the present description includes a method for operating an engine, comprising: operating an engine by injecting a gaseous fuel and a liquid fuel to at least an engine cylinder; diluting a mixture of at least an engine cylinder; and increasing a fraction of gaseous fuel relative to a fraction of liquid fuel injected to a cylinder in response to an operator tip-out.
By increasing injection of a gaseous fuel during a transient engine operating condition it may be possible to reduce engine misfires when the engine is operating at a higher dilution level. Further, an engine may be operated at higher dilution levels to improve fuel economy and emissions, at least under some conditions, when combustion stability can be improved during transient engine operating conditions. Increasing combustion stability can reduce the possibility of poor combustion stability and/or engine misfires, thereby improving drivability and/or decreasing engine emissions.
The present description may provide several advantages. Specifically, the approach may allow an engine to operate at higher charge dilution levels. As such, engine efficiency may be improved by the following method. Further, the method may reduce engine emissions during transient operating conditions.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.